Thurman believes Mayweather will probably win the fight (if it happens), but believes the Filipino boxer is the only challenger who could potentially spoil Mayweather's undefeated record.
Thurman gave an in-depth interview to On The Ropes Boxing about his take on the superfight the world has been waiting to see.
He said: "At the end of the day, nobody has the credentials that Floyd Mayweather has. Outside of Floyd Mayweather, nobody has the credentials that Manny Pacquiao has. You're still looking at two of the best fighters in this generation going at it. At the end of the day, real boxing fans like to see warriors and that's what Manny Pacquiao is. The fight is gonna be tremendous.
He added: "I still pick Mayweather, especially if the fight is happening at the MGM. Outside of that, Pacquiao needs to be the Pacquiao that made him famous. He needs to throw the punches, the combinations. We know that Pacquiao is better than Cotto and Cotto gave Mayweather one hell of a fight. I do see Pacquiao having a great chance of winning the fight, but I do believe that to truly win the fight he's gonna have to at least create one to two knockdown – A minimum of one knockdown to get that 10-8 round.
"I almost see the fight fifty-fifty, but I still see the fight more leaning in Mayweather's favor.
"I'm gonna favor Mayweather until someone shows me a reason not to – and maybe it will be Manny Pacquiao on May 2nd. I'll be cheering for both fighters, at the end of the day, I just want to see a great fight going down in the world of boxing."